1. Field of the Invention
The present general inventive concept relates to an apparatus and a method to generate a halftoning screen, and an image forming apparatus, and more particularly, to an apparatus and a method to generate a halftoning screen capable of reproducing both smooth and detailed tones, and an image forming apparatus to provide the same.
2. Description of the Related Art
Unlike multilevel-based imaging apparatuses, a binary level-based image forming apparatus expresses an image according to the presence and absence of dot output.
Accordingly, a “halftoning” or conversion into a binary level image is necessary, in order to reproduce a multilevel-based image through a binary level-based image forming apparatus.
Among a variety of halftoning methods, screening halftoning converts the grey level gradients 0 to 255 to a binary value by comparing them to a predetermined screen.
Mainly two types of screens are widely used, and these are an amplitude modulated (AM) screen and a frequency modulated (FM) screen. The AM screen outputs a cluster of dots, and thus provides more stable dots than the FM screen. These characteristics of the AM screen, often called a clustered screen, resulting in the screen to be widely adopted in many image forming apparatuses.
The AM screen determines locations of the dot centers and grows the dots with respect to the dot centers. Accordingly, lines per inch (LPI) and angle of a final form of screen table are determined depending on where the dot centers are located.
FIGS. 1A to 1D illustrate examples of a conventional AM screen.
FIG. 1A illustrates an AM screen having 141 LPI, and 232 grey level, and FIG. 1B illustrates an AM screen having 141 LPI and a 106 grey level. FIG. 1C illustrates an AM screen having 212 LPI and a 232 grey level, and FIG. 1D illustrates an AM screen having 212 LPI and a 106 grey level.
Referring to FIGS. 1A to 1D, a conventional AM screen is designed to keep the same LPI value throughout the entire input of grey levels 0 to 255. For example, if 141 LPI is set, all the input grey levels keep 141 LPI, and if 212 LPI is set, then all the input grey levels keep 212 LPI.
In the above example, the AM screen having 141 LPI is suitable to express smooth tone, but is not that efficient to express details. Meanwhile, the AM screen having 212 LPI is suitable fit for expressing details, but is not a good choice to reproduce a smooth tone.
However, users do not have a choice but to select either lower LPI or higher LPI, that is, to select the reproduction of either smooth tone or details.